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Many events in global tectonics and high latitude climate had significant effects on Cenozoic climate evolution. This chapter explores three revolutions in climate research that have dramatically altered our perception of global and African climate. First, the discovery that large magnitude climate events occurred abruptly, sometimes in as little as decades, has prompted high-resolution paleoclimate reconstructions and new conceptions of climate dynamics. Second, recent climate studies have revealed significant tropical climate variability. Modern observational climate data have indicated that the largest mode of global interannual climate variability is the El Niño Southern Oscillation in the tropical Pacific. Revised estimates of tropical sea surface temperatures during global cool and warm events have revealed significant tropical sensitivity to global climate change. Third, the role of the tropics in global climate change has been reconceptualized. This chapter also discusses the modern climate of Africa, abrupt events in the Paleocene, Oligocene Antarctic glaciation and Southern African climate, mid-Miocene climate change in Africa, plio-Pleistocene environmental change, cool and dry conditions during the Last Glacial Maximum, and Holocene climate.

Mangrove vegetation related to the modern tropical Asian palm, Nypa, was present along Africa's coasts at low latitudes in the Paleocene and Eocene, and pollen evidence of other palms is common. This chapter reviews and interprets the paleobotany and paleogeography of Africa during the Cenozoic. It presents a dynamic view of changes in plant communities and ecosystems through time, so that the evolutionary and biogeographic history of Cenozoic African mammals can be considered in the context of the communities to which they belonged. To facilitate this goal, the chapter explores environmental change in the context of major physiographic change such as graben formation associated with rifting in East Africa, and shows paleobotanical sites in their correct position on paleogeographic maps. A common challenge to providing a floral context for the mammalian fossil record stems from the fossilization process itself. The circumstances in which bones and plants become fossils are not often the same, and consequently they are rarely found together.

The chapter first shows carbon dioxide variability over long geological timescales. The current stocks and fluxes of carbon are then given, for the whole planet and for the atmosphere, ocean and land separately. The main flows of carbon in the ocean, through the biological pump (via uptake through photosynthesis) and the physical pump (via involving chemical transformation uptake in water and production of carbonate), and on land, through photosynthesis (Gross Primary Production) and respiration leading to Net Primary Production, Net Ecosystem Production and Net Biome Production and through the storage of carbon in biomass, are described. Next, carbon interactions during the Paleocene–Eocene Thermal Maximum and glacial–interglacial transitions, thought to involve changes in ocean circulation and upwelling, are examined. The key changes from anthropogenic perturbation of the natural carbon cycle are shown to be due to fossil fuel burning and land-use change (deforestation). The effects of the carbon–climate feedback on temperature and carbon stocks are also shown.

Details Blur As We peer back through millions of years, but the outline of the story is clear enough. During the past 2– 3 million years, our hominin forebears had to cope with an increasingly vari-able and cooling climate. Across those 100,000 Homo generations, survival and reproduction depended on maintaining biological and behavioral compatibility with constantly changing climatic and environmental conditions. Hence much of modern human biological versatility and adaptability, including several unique aspects of brain function, comes from evolution’s selective winnowing within those ancient predecessor populations. The genes of the survivors, those best able to reproduce, are part of our genetic inheritance today. That climate change has been a major source of natural selective pressure has long been known. Alfred Russel Wallace, the overshadowed younger contemporary of Charles Darwin and codiscoverer of evolution by natural selection, wrote that, among the variations occurring in every fresh generation, survival of the fittest occurred in response to the “changes of climate, of food, of enemies always in progress.” The corollary, of course, is that since biological evolution must focus on surviving the present, oblivious of the future, it provides no guarantee against extinction. Even so, a multivalent brain that enables cultural and behavioral adaptability and strategic forward thinking would surely help an animal species cope better with subsequent environmental changes. Indeed, it seems to have worked sufficiently well for our Homo genus ancestors during two million years of ever-changing climatic conditions for at least one Homo species to have carried the baton of survival into the present. In the next two centuries, our species faces a new challenge of greater, faster, and protracted climate change. Since the Cambrian Explosion of new life forms around 540 million years ago, there have been five great natural extinctions and many lesser ones. The earliest extinction of multicellular life, though less destructive than its successors, occurred around 510 million years ago, apparently due to acute sulfurous shrouding, cooling, and oxygen deprivation caused by a massive volcanic eruption in northwest Australia. Most of these catastrophic transitions were marked by climate extremes, volcanic activity, and altered ocean chemistry, especially rapid surface acidification of shallow coastal waters.

The central grassland region of North America (Fig. 1.1) is the largest contiguous grassland environment on earth. Prior to European settlement, it was a vast, treeless area characterized by dense head-high grasses in the wet eastern portion, and very short sparse grasses in the dry west. As settlers swept across the area, they replaced native grasslands with croplands, most intensively in the east, and less so in the west (Fig. 1.2). The most drought-prone and least productive areas have survived as native grasslands, and the shortgrass steppe occupies the warmest, driest, least productive locations. James Michener (1974) provided an apt description of the harshness of the shortgrass region in his book Centennial:… It is not a hospitable land, like that farther east in Kansas or back near the Appalachians. It is mean and gravelly and hard to work. It lacks an adequate topsoil for plowing. It is devoid of trees or easy shelter. A family could wander for weeks and never 4 nd enough wood to build a house. (p. 64)… The objective of this chapter is to introduce the shortgrass steppe (Fig. 1.3) and its record of ecological research. First we present an ecological history of the shortgrass steppe since the Tertiary, and provide the geographic and climatic context for the region. Second we describe the major research sites, and the history of the three major entities or programs that have shaped much of the science done in the shortgrass steppe: the U.S. Department of Agriculture (USDA)–Agricultural Research Service (ARS), the International Biological Programme (IBP), and the Long-Term Ecological Research (LTER) Program. Grasses have been an important component of the shortgrass steppe of North America since the Miocene (5–24 million years ago) (Axelrod, 1985; Stebbins, 1981). Before that, during the Paleocene and Eocene (34–65 million years ago), the vegetation was a mixture of temperate and tropical mesophytic forests. Two causes have been proposed as explanations for this ancient change from forest to grassland. First, global temperatures decreased rapidly during the Oligocene (24–34 million years ago), creating conditions for a drier climate. These drier conditions, combined with a renewal of the uplift of the Rocky Mountains that had begun during the Paleocene, left the Great Plains in a rain shadow.

In 2015, the annual mean global atmospheric carbon dioxide (CO2) level surpassed 400 parts per million (ppm; Figure 1.1), and we know very well that this rise is caused by human activities (Figure 1.2). It was the first time in 3 million years that such a level had been reached. Crossing this level has caused widespread concern among climate scientists, and not least among those called pale climatologists, who work on natural climate variability in prehistoric times, before humans. Over the last few decades, researchers have been repeatedly raising the alarm that emissions of CO2, along with those of other greenhouse gases, are getting dangerously out of control and that urgent remedial action is needed. With the crossing of the 400 ppm threshold, this sense of urgency reached a climax: at the Conference of Parties 21 meeting in Paris—also known as COP21 or the 2015 Paris Climate Conference—broad interna¬tional political agreement was reached to limit global warming to a maximum of 2°C, and if at all possible 1.5° C, by the end of this century. If one calculates this through, this implies a commitment for society to operate on zero net carbon emissions well before 2050, along with development and large-scale application of methods for CO2 removal from the climate system. (Scientists focus on carbon (C) emissions when they discuss emissions because it helps in calculating CO2 changes produced by the processing of specific volumes/ masses of fossil fuel hydrocarbons.) Clearly, the challenge is enormous, especially given that even implementing all the pledges made since COP21 would still allow warming to reach about 3°C by 2100. But, regardless, the agreement was ground breaking. It was a marker of hope, optimism, and international motivation to tackle climate change. Moreover, there are concerns about the stated COP21 targets. First, the proposed 2°C or 1.5°C limits to avoid 2 “dangerous” climate impacts may sound good, but there is no specific scientific basis for picking these particular numbers. Second, the implied “end of this century” deadline is an arbitrary moment in time.